Cord Reel Variable Current Thermal Management and Damage Detection

ABSTRACT

A battery charging assembly includes a load management system, a charging cord with a battery connector, and circuitry for detecting cord removal or damage. The load management system monitors the heat buildup in a coiled portion of the charging cord and issues a corresponding signal to control the current flowing through the cord.

FIELD OF THE INVENTION

The present invention relates generally to management of the generation of heat in a retractable cord reel apparatus delivering electrical power, and more specifically to insuring that the flow of electrical current in a cord which may be partially or fully coiled on a reel does not result in generation of excessive heat which could damage the cord, reduce its useful life, or create danger to the user. Cords used for charging batteries in, for example, electric vehicles, are frequently coiled when not in use to safely store the cord and protect it from the elements and damage.

A retractable cord reel may be part of a charging station in, for example, a parking lot at an airport or in a home or office garage. The charging station may be a post or other suitable structure containing the cord reel and associated circuitry. If used in a public location, storing the cord on a reel helps protect against theft of the cord for its copper, because the charging station can require use of a key card or similar means to allow use of the station.

The cord may be only partially unreeled when used to charge a battery. Heat generated by the flow of current will not escape as readily from a cord carrying electrical current when the cord is partially or completely coiled. As the amount of cord on the reel increases, more heat tends to be trapped. Overheating could occur even if the cord is simply looped over a hook, rather than being stored on a rotating reel.

The cord reel assembly described here includes improved features for limiting the current flow in the cord, with higher currents being permitted if the cord is substantially or fully unreeled, and for sensing the temperature of the reeled cord at one or more locations. Current flow therefore need not be limited to an unnecessarily low value suitable for a cord that is fully coiled. Higher currents, and therefore shorter charging times, are made possible.

BACKGROUND OF THE INVENTION

Retractable cord reels have been used in various applications to retractably store various types of cables. Typically, a reel might have a stationary end and a retractable end, the retractable end capable of extension from and retraction back into the reel, and which can be connected to, for example, a battery in an electric vehicle. Using a reel provides convenient storage for the cord. The reel also protects the cord from damage, since it need not be left on the ground. Damage to the cord is reduced. The hazard presented to a user by a damaged electrical cord is also avoided.

The use of a reel has a disadvantage, because the flow of current generates heat in the cord. A larger current tends to generate more heat. One application is a charging station for an electric vehicle. If the user parks his electric vehicle very close to the charging station, or if the vehicle is small, it may not be necessary to unreel more than a short length of cord sufficient to reach the battery connector on the vehicle. As current flows from the charging station to the vehicle, heat will be generated in the cord. Because most of the cord is coiled on the reel, heat cannot escape as readily, and the cord temperature can rise, possibly to the point where the function of the charging station, or the safety of the user, is jeopardized. An additional factor is the lack of experience or knowledge on the part of many vehicle operators.

DEFINITION OF TERMS

The following terms are used in the claims of the patent as filed and are intended to have their broadest plain and ordinary meaning consistent with the requirements of the law:

A “retractable cord reel” refers to a cable storage unit and cable management systems having a spooling cord such as the type found in U.S. Pat. No. 5,094,396 to Burke, the subject matter of which is hereby incorporated by reference, and U.S. Patent Application No. 2007/0262185 to Burke, the subject matter of which is also hereby incorporated by reference.

An electric vehicle means any vehicle, including one propelled solely by a rechargeable battery, and one using hybrid propulsion including a rechargeable battery.

Where alternative meanings are possible, the broadest meaning is intended. All words used in the claims set forth below are intended for use in the normal, customary usage of grammar and the English language.

SUMMARY OF THE INVENTION

The present invention relates to one or more of the following features, elements or combinations thereof.

One disclosed embodiment is directed to improvements in a retractable cord reel for battery charging stations, including those used for vehicles propelled at least in part by rechargeable batteries. The charging station includes an electric cord connected to a source of power. An end of the cord has a vehicle connector assembly. Control circuitry regulates the current supplied to the battery being charged. The reel has one or more temperature sensors for determining the thermal buildup in the cord. The control circuitry includes a processor that receives an input signal from one or more of the sensors. The processor issues an output signal that is related to the input signal from the sensor or sensors. The output signal limits the charging current being supplied to the battery, so that the cord does not overheat. Heat generated in the cord is safely dissipated.

In another embodiment, the disclosed apparatus includes a sensor for determining the amount of cord that has been unreeled. As the length of unreeled cord increases, the processor receives an input signal representative of the length of unreeled cord, and issues an output signal increasing the maximum allowable current to the battery being charged.

Thus, it can be seen that one object of the disclosed invention is to provide a mechanism for the avoidance of overheating a battery charging station, and in particular the charging cord.

A further object of the present invention is to allow the maximum charging current to be delivered to the battery being charged.

Another object of the invention is to detect damage to the cord, or removal of the cord.

It should be noted that not every embodiment of the claimed invention will accomplish each of the objects of the invention set forth above. For instance, certain claimed embodiments of the invention will not require a temperature sensing device. In addition, further objects of the invention will become apparent based upon the summary of the invention, the detailed description of preferred embodiments, and as illustrated in the accompanying drawings. Such objects, features, and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, and as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a charging station with a cord reel cord reel assembly according to one embodiment of the present invention; and,

FIG. 2 is a block diagram of a board assembly used with an alternative sensor embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

As can be seen in FIG. 1, a charging system 10 includes an alternating current (AC), 120 volt power input 12. AC power is connected to a relay 14, which in this case is a double-pole, single throw switch that makes or breaks connections between power input 12 and a vehicle connector 16. Those of skill will understand that the relay can include connection for either or both of AC-Line and AC Neutral and/or LINE2 (for the case of a Level 2 charger). In this embodiment, because the battery is used for propulsion in a vehicle, vehicle connector 16 is constructed in accordance with SAE Surface Vehicle Recommended Practice J1772, “SAE Electric Vehicle Conductive Charge Coupler,” issued by the Society of Automotive Engineers for electric vehicles. For different applications not involving an electric vehicle, connector 16 need not comply with J1772, and its design can be modified as required by the intended use.

Connector 16 includes electrical connections for ground 18, AC line 20, AC neutral 22 and pilot signal 24. A current transformer 28 is used for ground fault interruption to protect a user from injury. Relay 14, pilot signal 24, and current transformer 28 are connected to board assembly 26. Board assembly 26 controls whether relay 14 is open or closed. The AC connect input between relay 14 and a microcontroller 38 on board assembly 26 may signal microcontroller 38 whether relay 14 is open or closed.

When used for charging an electric vehicle, the preferred embodiment of the system described herein is a Level 1 charger, as that functionality is described by the California Air Resources Board and codified in title 13 of the California Code of Regulations, the U.S. 1999 National Electrical Code section 625 and in SAE International standards. Such systems use lower voltage and are therefore less expensive and suitable for use at a home or other locations where 120 volt AC power is readily available. Due to the relatively low voltage, charging times are longer, possibly as much as ten to twelve hours for a full recharge of an electric vehicle battery. However, those of skill will understand that the present invention as defined by the claims covers not only Level 1 chargers, but also chargers designated as (for instance) Level 2 under those same standards.

The pilot signal for an electric vehicle application according to SAE standard J1772 is a square wave signal with a frequency of one kilohertz. It varies in amplitude between plus and minus 12 volts. A 12 volt power supply 30 provides a reference voltage for the pilot signal 24. Power supply 30 also provides power for microcontroller 38 on board assembly 26. The pilot signal 24 communicates between the vehicle and the board assembly 26. Pilot signal 24 controls the amount of current delivered to the vehicle battery being charged. The amount of current is varied by altering the duty cycle of the square wave, that is, the pulse duration divided by the pulse period. A lookup table stored in the electric vehicle contains the variation in the duty cycle necessary for a given current, though those of skill will understand that the duty cycle could alternatively be generated by an algorithm “on the fly” by using the teaching of the present invention. For example, a duty cycle of 26.7% correlates to a current of 16 amperes under the J1772 standard.

The duty cycle is also varied in the present embodiment according to the amount of cord that is unreeled. The amount may be determined directly or indirectly. For example, a potentiometer 46 can be used, which will indicate how much of the cord is unreeled, and therefore indirectly indicate the amount of heat that will be generated in the reeled portion of the cord. A direct measurement of heat generation in the reeled cord can be determined by a thermistor, a thermocouple, or digital temperature sensor 40 installed in the cord reel as shown in FIG. 2. Third, the current transformer 28 and a sensor of reel rotation 46 may be employed with a lookup table stored in the microcontroller 38 identifying the maximum current for a given length of unreeled cord.

Regardless of the type of sensor, the sensor signal is delivered to board assembly 26, as shown in FIG. 2. In this embodiment, board assembly 26 includes an AC relay control 32 that controls relay 14. A pilot driver 34 is on board assembly 26. Driver 34 modulates the pilot signal duty cycle to control the amount of current flowing through the cord to the vehicle battery. A pilot level shifter 36 on board assembly 26 can receive a signal from the car to confirm or determine, for instance, the current required to bring the car battery to a full charge. Temperature sensor input 42 receives a signal from a potentiometer, thermistor or digital temperature sensor 40 as shown in FIG. 2. Ground fault detection circuit 44 receives an input from current transformer 28. Detection of a fault causes microcontroller 38 to open relay 14, shutting off current.

Relay control 32, driver 34, shifter 36, sensor input 42, and detection circuit 44 are connected to microcontroller 38 which can be programmed by one of skill in the art. One suitable microcontroller is an Atmel ATMEGA328P from Atmel Corporation of San Jose, Calif.

While the disclosure is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and have herein been described in detail. It should be understood, however, that there is no intent to limit the disclosure to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims. 

What is claimed is:
 1. A vehicle charging system (10) including a load management mechanism for providing a limitation on the current supplied to an electric vehicle, the system comprising: a) An electric cord and vehicle connector assembly (16); b) A pilot signal provided via the electric cord and vehicle connector assembly (24) for regulating the current supplied to the electric vehicle; c) A sensor for determining the thermal buildup in the electric cord and vehicle connector assembly (42); and d) A processor (38) located on the vehicle charging system for receiving an input from the sensor correlating to the thermal buildup in the electric cord and vehicle connector assembly, the processor modifying the pilot signal based upon such input so as to limit the level of current being supplied to the electric vehicle.
 2. The vehicle charging system of claim 1 wherein the electric cord and vehicle connector assembly comprises a retractable cord reel including a spool for retracting and extending an electrical cord for supplying a charge to an electric vehicle.
 3. The vehicle charging system of claim 2 wherein the sensor for determining the thermal buildup in the electric cord and vehicle connector assembly comprises a sensor for determining the extent to which the retractable cord reel has been extracted from the spool.
 4. The vehicle charging system of claim 2, wherein the sensor for determining the thermal buildup in the electric cord and vehicle connector assembly comprises a thermistor for measuring the temperature proximate to the spool.
 5. The vehicle charging system of claim 2, wherein the sensor for determining the thermal buildup in the electric cord and vehicle connector assembly comprises a digital temperature sensor for measuring the temperature proximate to the spool.
 6. The vehicle charging of claim 1 further comprising a detection conductor in the cord, the detection conductor being operatively connected at one end to the processor, and at the other end to a resistor in the vehicle connector assembly. 